Image intensifier tube



Jan. 19, 1954 R. L. LoNGlNl 2,665,864

IMAGE INTENSIFIER TUBE Filed aan. 2o, `195o All All

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Cesio# ed Amimony Aiumnum INVENTOR WTNESSES: zinc sulpmde T' //j/W nxide cemposiee Layer RichordL. Longml.

. l BY ATTORNE im. a

Patented Jan. 19, .1954

llVIAGE INTENSIFIER TUBE Richard L. Longini, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 20, 1950, Serial No. 139,715

Claims. 1

My invention relates to structures for image intensiers of the general type shown in Longini and Hunter Patent 2,555,545 issued June 5, 1951, and assigned to the Westinghouse Electric Corporation of East Pittsburgh, Pennsylvania.

Such image intensiers are provided at one end with a fluorescent screen in close contiguity to a photoelectrically emissive surface, and at the other end with a phosphor screen adapted to emit light when electrons impinge upon it. In such arrangements a light image is excited on the uorescent screen, which, in turn, generates an electron image on the contiguous photoelectric surface. The electrons forming the last-mentioned image are accelerated to high velocities and focused by an electron lens system on a phosphor screen on the other end of the tube producing there a light image, preferably of smaller dimensions but much higher intensity, than the light image on the fluorescent screen. The high intensity light image on the phosphor screen is viewed through a suitable lens system to obtain an intensied replica of the image excited on the fluorescent screen. An image intensifier tube of the type just described is illustrated in Fig. l of this application. The manufacture of image intensiiers of the type just described presents many difficult problems, and the inventions which I herein describe are eective solutions of some of these. For example, it is naturally necessary to utilize an eicient photoelectric emission from the photoelectric surface at the input end of the intensifier; and for this reason it is highly desirable to employ a cesiated surface, such as cesiated antimony CsaSb. It is likewise desirable to utilize for the output screen on which the electrons impinge the most eiicient phosphors; and for this purpose I have found zinc-cadmium sulphide phosphors desirable. However, the cesiated antimony surface on the input screen can be applied only after the component parts of the intensier tube envelope have been completely assembled and exhausted to a high degree. The surface of the input screen is coated with antimony by sublimation in the highly exhausted envelope and cesium then likewise vaporized in the exhausted envelope to deposit on the antimony surface.

One object of my invention is, accordingly, to provide means for preventing cesium vapor undergoing deposition on the photoelectric surface at the input screen from reaching and destroying the phosphors at the output screen.

Another object of my invention is to provide the surfaces of the electron lens components and other metallic parts Within the image intensifier tube with a surface finish which shall be subisjtantially non-reflective to any stray light in the ube.

Other objects of my invention will become apparent upon reading the following description, taken in connection with the drawing in which:

Figure 1 is a cross-sectional view of a schematic type showing an image intensifier embodying the principles of my invention; and

Fig. 2 is a detail view in cross-section of the wall of elements forming an electron-lens system in Fig. 1.

Fig. 3 is an enlarged vieW in section of a portion of the input screen of the tube of Fig. 1.

Referring in detail to Fig. 1, the image intensier comprises a glass envelope l subdivided into three sections which are joined vacuum tight to each other by two gasket seals 2 and 3. The gasket seals 2 and 3 each comprises a pair of annular metallic members with a gasket of gold interposed between them against which they are tightly clamped by suitable bolts or other means (not shown). The metal rings are welded to rings 4, 5 and E ofthe alloy Kovar which are sealed to the glass portions of the envelope in accordance with the application, Serial` No. 80,377, of R. O. McIntosh, led March 9, 1949, and assigned to the Westinghouse Electric Corporation.

At the smaller end of the container I is positioned the output screen l which comprises a glass diaphragm coated on its interior surfacey with the phosphor zinc-cadmium sulphide, which latter is coated in turn with a thin layer of aluminum. Such output screens are described in more detail in Hushley and Siebert Patent 2,533,809 issued on or about December l2, 1950, for Protection of Phosphors from Attack by Alkali Vapors, and assigned to the Westinghouse Electric Corporation. At the opposite end of thev of the envelope i is positioned the input screen 8 which comprises a thin sheet of aluminum which may, as shown, be slightly concave and which has on its inner face a thin layer of iiuorescent.-

material. Features of the screen 8 are described in greater detail and claimed in Coltman and Longini Patent 2,606,299 issued August 5, 1952.

As Fig. 3 shows the screen 8 is surfaced with a The support rods 9 may be attached to the glass 3 envelope by metal cups II sealed to tubulations I2 on the glass envelope. Such seals and structure are completed before the separate gasket seals 2 and 3 have been assembled in position and made vacuum tight.

The envelope I is provided with a number of tubulations I2 through which support rods and in-leading wires for the components of the electron lens system may be passed through the walls of tube I. The electron lens system comprises I annular metal conductors I 3 which are supported on metal rods sealed to the tubulations I2 by metal cups such as have already been shown at II.

The antimony and cesium are deposited on the screen 8 only after the tube structure so far' described has been assembled, made vacuum tight, and heat treated in the evacuating furnace to outgas its parts. The screen 8 and the components I3 of the electron lens system are assembled on a fixture which holds them in the desired alignment. The fixture is then withdrawn from position in the lens system, and the input end of the envelope connected to the output end by joining the annular components 2 of the gasket seal. The output screen 'I is completed and attached to one ring of the gasket seal 3 before installation in the tube. The two parts of the gasket seal 3 are then clamped together. One of the tubulations I2 is provided with a metal tube supported on a metal seal, and the evacuating pumping system is connected to this tube. Two others of the tubulations I2 are respectively provided with inlet conduits, through one of which a suitable boat containing antimony may be moved through a hole in the adiacent component I3 into the axial region of the container I in front of the input screen. Through the other tubulation a small capsule from which the cesium vapor may be evolved by heat is likewise pushed through a similar hole in said component into the axial region in front of the input screen.

After the container I is thoroughly exhausted and heat treated to outgas its interior surface, the antimony boat is pushed into position in front of the input screen and heated so that its vapor condenses in a thin layer all over the concave surface of the screen. The container vfor the antimony is then withdrawn from the tube, and the capsule containing the cesium is advanced to the axial position whence the tube is heated sufficiently sc that the evaporating cesium reacts with the antimony surface. It is likewise thereafter withdrawn from the envelope I and the conduits through which the antimony and cesium were introduced are sealed ofi' outside the tube.

In order to prevent the cesium vapor in front of the input screen 8 from migrating to the output screen I and there deteriorating the phosphor, the surfaces of the annular components I3 ofthe electron lens system are coated with carbon. This coating may be eifected by moving a small acetylene flame over the surfaces to be coated at any time before the tube is assembled. While I do not wish to be bound by any theory I may advance as to the mode of operation of the present invention, my present opinion is that any cesium molecules which strike the carbon coated surfaces are held 'to the latter by adsorption.

During the above-described process of photosensitizing, the input screen must be maintained at an elevated temperature of about 130 C. At this temperature some cesium molecules adsorbed in the carbon coating of the elements near the cathode will tend to evaporate. I have found it possible to minimize the probability that this will cause cesium molecules to migrate to the phosphor at the output screen 'I if the tube in the immediate vicinity thereof is maintained cool, for example at a temperature of about 60 C. Such cooling maintains the tube elements including the components of the electron lens system which are nearer the output screen 'I at a substantially lower temperature than those in the immediate vicinity of the input screen 8.

While I have found so far that the carbon deposited from an acetylene flame is a most effective adsorbing agent, I have also tried other materials with success. For example, zinc sulphide powder may be sprayed on the elements of the electron lens system to provide such a cesium-holding surface.. I have also found that tin oxide painted on the metal surfaces as a suspension in a volatile liquid also is a fairly satisfactory adsorbing agent.

The presence of the above adsorbing agents on the surface of the electron lens elements likewise renders them good light adsorbers, the zinc sulphide and tin oxide turn black on reacting with cesium introduced in later steps already described, so that ii any stray light enters the image intensifier tube, it is adsorbed and not reflected from the metallic element surfaces I3 to the photosensitive surface of the screen 8. The presence of such random reflection of light to the photosensitive surface would cause an undesired emission of electrons which would tend to at least partially mask the electron image due to the light emitted from the fluorescent layer of the screen 8 when in use.

These materials deposited on the elements I3 also render them poor photoelectric and secondary emitting surfaces. As the antimonyv and cesium are evaporated forming the photosensitized surface, some is also deposited on elements I3 causing them to have a photoelectric response unless they are suitably desensitized. The deposit of cesium or antimony also enhance the secondary emission from these surfaces. Any such emission from the cylinders I3 cause additional undesired disturbing backgro'unds for the image on vthe output screen 'I.

I claim as my invention:

l. An image intensifier device comprising an evacuated container having at one end .a screen which emits light in-response to incidence of moving electrons and having at the other end an input screen comprising va support, a first layer comprising a substance which emits light in" response to an incident radiation and another layer' adjacent thereto which is photoelectrically emissive, and an electron lens system between saidr screens comprising .conducting members havingsurfac'esof zinc sulphide.

2'. In image intensifier device comprising ani evacuated container having at onelend a screen whichemits light in response'to incidence of moving electrons and having at the other end an input screen comprising a support, a rstA layer comprising a substance which emits lightl in response to an incident radiation and another layer adjacent thereto which is photoelectrically emissive, and an electron lens system betweensaid screens comprising annular metallic members having surfacesgof zinc sulphide.

3`. The method of preserving from deterioration Zinc-cadmium-sulphide positioned inthe same container with a cesiated atmosphere which comlprises coating elements located in said container near said zinc-cadmium-sulphide with carbon by bringing their surfaces into contact with an acetylene flame.

4. The method of cesiating an element positioned in the same container with a phosphor which comprises providing carbon surfaces on elements located in said container near said phosphcr and maintaining said phosphor at a relatively lower temperature while providing cesium heated to a relatively higher temperature.

5. An image intensiiier device comprising an evacuated container having at one end a screen which emits light in response to incidence of moving electrons and having at the other end an input screen comprising a support, a first layer comprising a substance which emits light .in response to an incident radiation and a cesiated layer adjacent thereto which is photoelectrically emissive, and an electron lens system between said screens comprising conducting members having surfaces of a substance which holds cesium molecules.

6. An image intensifier device comprising an evacuated container having at one end a screen which emits light in response to incidence of moving electrons and having at the other end an input screen comprising a support, a rst layer comprising a substance which emits light in respense to an incident radiation and another layer adjacent thereto which is photoelectrically emissive, and an electron lens system between said screens comprising conducting members having surfaces which have been coated with tin oxide.

7 The method of preserving from deterioration the surface of a phosphor positioned in the same container with a cesiated atmosphere which comprises coating elements in said container near said phosphor with a suspension of tin oxide in a volatile liquid.

8. The method of preserving` from deterioration the surface of a substance which reacts with cesium when positioned in the same container with a cesiated atmosphere which comprises coating elements located in said container near said substance with carbon.

9. The method of preserving from deterioration the surface or" a substance which reacts with cesium when positioned in the same container with a cesiated atmosphere which comprises coating elements located in said container near said substance with a substance which exerts a holding power on cesium.

l0. The method of cesiating an element positioned in the same container with a substance which is deteriorated by cesium which comprises providing carbon surfaces on elements located in said container near said substance and maintaining said substance at a relatively lower tem- 6 perature while providing cesium heated to a relatively higher temperature.

11. The method of cesiating an element positioned in the same container with a substance Which is deteriorated by cesium which comprises providing surfaces of a substance which exerts a holding power on cesium on elements located in said container near said substance and maintaining said substance at a relatively lower temperature While providing cesium heated to a relatively higher temperature.

12. The method of cesiating an element positioned in the same container' with a phosphor which comprises providing surfaces of carbon on elements located in said container near said phosphor, maintaining said phosphor at a temperature of around C., and at the same time heating cesium located Within said container at a point removed from said phosphor to a ternperature of around C.

13. The method of oesiating an element positioned in the same container with a substance which is deteriorated by cesium which comprises providing carbon surfaces on elements located in said container near said substance and maintaining said substance at a temperature of around 60 C. while another portion of said container in which cesium is positioned is heated to a temperature of aro-und 130 C.

14. The method of oesiating an element positioned in the same container with a substance Which is deteriorated by cesium which comprises providing surfaces of a substance which exerts a holding power of cesium on elements located in said container near said substances and maintaining said Substances at a temperature of around 60 C. While another portion of said container containing cesium is heated to a temperature of around 130 C.

15. In combination with a vacuum-tight container, a zinc-cadmiuzn-sulphide surface and a cesiated surface therein separated by an intervening space therein, and carbon-coated metal structures positioned in said space.

RICHARD L. LONGINI.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,151,992 Schwartz Mar. 28, 1939 2,158,853 Coolidge May 16', 1939 2,193,600 Mouromtse et al. Mar. 12, 1940 2,198,479 Langmuir Apr. 23, 1940 2,291,406 Paehr July 28, 1942 2,297,478 Kallmann Sept. 29, 1942 2,305,452 Kallmann Dec. 15, 1942 2,348,045 Wooten May 2, 1944 2,358,542 Thompson Sept. 19, 1944 2,501,882 Trunys et al Mar. 28, 1950 

